In recent years, self-steering axle suspension systems, particularly in the medium and heavy duty truck and semi-trailer industry, have become quite popular. Generally speaking, such suspensions are made self-steering by adjusting the pitch or caster angle of the wheels so that the drag of the wheels as the vehicle proceeds in the forward direction causes the suspension (i.e. the wheels of the system) to steer automatically in response to steering of the vehicle. Typical of such suspensions are those referred to as "pusher", "tag" or "trailing" axles found on trucks and semi-trailers. They may be of the liftable or non-liftable type.
In most self-steering suspensions in common use, a steering damper or pair of dampers is used to suppress (dampen) oscillations during road operation of the vehicle. While such dampers come in a wide variety of styles, one known type is similar in construction to a conventional shock absorber either with, or without, an external auxiliary coil spring. Such devices are often referred to as "stabilizers". In such a damper, a large cylinder is provided which houses a fluid reservoir that is almost completely filled with a hydraulic (i.e. incompressible) fluid. This cylinder is separated into two compartments by a piston having an orifice, or orifices, in its head, thus to form a flow path between the two compartments, but which otherwise seals the two compartments against fluid flow therebetween. Dampening is accomplished by attaching one end of the cylinder (usually by a piston rod connected to the piston head) to the steering mechanism of the suspension and the other end to the axle or beam structure of the suspension or vehicle (or vice versa). Since the orifice(s) in the piston head restricts flow between the two compartments as the piston slides in the cylinder due to oscillations experienced during vehicle operation (e.g. road shocks and wheel "shimmy"), such oscillations are appropriately dampened and tracking is stabilized.
In self-steering suspensions the castor angle, as aforesaid, is appropriately adjusted, in a conventional manner, to create steering during vehicle forward motion (e.g. as the vehicle goes into a turn). When the vehicle is backed up, however, the castor angle is no longer correct and the tires may tend to track improperly. In fact, the tires may actually tend to steer completely to one side or the other, at times quite abruptly. This, of course, is an undesirable occurrence, which may give rise to maneuverability difficulties or suspension damage.
Several technologies have been developed to address the aforesaid problem. The most common is to use some form of a mechanical linkage which locks out the steerability of the suspension (i.e. the wheels) when the vehicle is placed in its reverse operating mode. Two currently known systems in use are the so-called "bar lock" and "pin lock" systems.
In the "bar lock" system, a bar (or, more appropriately, a locking arm) is caused to swing into locking position by air actuation employing appropriate valving off of the brake chamber. When the locking arm swings into place, it engages an opening in the tie bar plate of the suspension's steering mechanism. Since this plate is attached to the tie rod of the steering mechanism and the arm is ultimately attached to the axle, steering is prevented. The "pin lock" is somewhat similar to the bar lock system in that it operates under the same principle, but uses an actuated pin instead of a bar. When an air cylinder is actuated, it forces a spring loaded pin to move down through an opening in the tie bar plate, thus rendering the steering mechanism inoperative.
The various lockout devices and techniques known prior to the subject invention have one or more drawbacks associated with their use. For the most part, they are usually difficult to install, are heavy and complex in the number of parts required to be added to the suspension as additional items, and often require considerable maintenance. Some have the potential for unreliable lockout engagement, and many require the use of added shock absorbers or dampers because they, themselves, have no capability in this regard.
in view of the above, it is apparent that there exists a need in the art for a lockout mechanism which is not subject to the above drawbacks in the prior art. It is a purpose of this invention to fulfill this-need in the art, as well as other needs which will become more apparent to the skilled artisan once given the following disclosure.